There are multiple solutions in the art for the detection of anomalies, including bugging devices.
For example, a digital multi-meter (DMM) may be used to measure the voltage on a phone line, the current when the phone is on and off the hook, and the resistance of the telephone. The telephone is referred to herein as a customer purchased equipment (CPE). The DMM can perform some very basic functional tests to measure the electrical characteristics of equipment, such as how much power the device is using and if there is another device drawing power from a phone line. If the bugging device is primitive enough to draw too much current and load the phone line down, then the DMM can detect it and compare the current draw to a known good phone, thereby allowing the DMM to flag the anomaly.
The DMM can also be used with an Audio Generator Set to trigger primitive bugs into going into their active mode. In some cases the bug will immediately start sending signals down the line which can be picked up by the DMM. An Audio Spectrum Analyzer is adapted to the low end of the frequency range, encompassing audio to ultrasonic frequencies (20 Hz-5 MHz) which may be transmitted down phone and power lines.
A Time Domain Reflectometer (TDR) is a device that can determine if there are any deviations in electrical characteristics of a cable and can report the location of the disturbance in the cable. The graph of the response can be quite complex to interpret for a human user. The TDR signal is often blocked by electrical devices, such as a phone, thus rendering it ineffective in locating bugs past certain types of devices. In some cases, bugs can use this to their advantage to “mask” themselves. TDR measurements are also sensitive to cable attenuation. That is, the farther the fault is from the TDR, the lower the response signal that comes back to the device, and large impedance mismatches or diminish the available return signal. Thus, the technician has to sequentially fix the faults in order to look further down the line. In order to perform TDR measurements, the line also has to be taken out of service.
An RF Field Strength Detector (FSD) is used to determine if there are electrically active devices (bugs) clipped to or installed in “innocent” devices or cables. The RF FSD will only catch “noisy” bugs, such as continuously transmitting devices, or devices that have microprocessors continuously running and are not sufficiently shielded. The quieter the bugging device, the closer the RF FSD has to be to it to register a signal.
An RF Spectrum Analyzer (SA) is a much more sophisticated version of the RF. An RF SA is used to sweep through the RF frequency band to locate any potentially radiating devices, such as bugs. The biggest problem with this method is that the RF spectrum is very active, therefore locating the source becomes difficult. Even with a sophisticated signal analysis package, if the bug only transmits in a timed burst mode using spread spectrum techniques (say once a day at any given time), the likelihood of detecting it in an unshielded room using the RF SA is virtually impossible.
Of the four technologies, the TDR, the RF FSD, and the RF SA can determine the approximate location of an anomaly, though none can definitely identify its nature. In the case of the RF FSD and RF SA, the bugging device has to be noisy enough and on long enough for it to be picked up. In the case of the TDR, multiple reflections can often cause a very complicated pattern that is difficult to interpret. The TDR also has an attenuation problem due to the relatively small amount of energy that is available in the step pulse to detect line impedance anomalies.
In use, the RF SA has to be coupled with a sophisticated data extraction and analysis package since the RF bug could be transmitting just about anywhere in the RF spectrum. Newer technologies have made it much more difficult to detect such devices, as they can illegally use mobile phone frequencies, ISM bands, and spread spectrum techniques with data squirts to hide themselves from a simple RF sweep. Often a long duration test coupled with multiple antenna locations to perform relative signal strength measurements to subtract background noise is required, and even then the bug may escape detection.
Tone generator/receiver devices work by generating a series of signals that are sent down the wire and an integrated receiver picks up the returned power from the other line. Most of the devices have a series of discrete or other “proprietary” tones, and are designed to stimulate either the TIP or RING lead only while detecting the signal that is coupled into the other line. These signal levels are then put through a mathematical algorithm that generates a number which corresponds to the overall response of the line to the series of tones.
Generally the tone receivers work over a fixed, discrete set of waveforms, and use a simple RMS style power envelope detector for recovering the received signal. The detector function is relatively broadband, so that even though there is only one tone being sent out, the detector will pick up any other additional noise on the line. These are handheld devices with no memory or database connectivity that are designed for intermittent manual use, as they also require the phone line to be disconnected during testing.
Thus, it is desirable to provide a method and apparatus for detecting surveillance devices on a telephone line that employs continuous monitoring. Additionally, it is also desirable to provide a method and apparatus for detecting surveillance devices that does not require an operator. Finally, it is also desirous to provide a method and apparatus for detecting surveillance devices that may be employed without disrupting use of the telephone line.